Seasonal Variability of Dissolved Organic Substances Content in the Water of the Kuibyshev Reservoir

Abstract

The purpose is to study the characteristics of seasonal variability in the content of dissolved organic matter (DOM) in the water of the Kuibyshev Reservoir and the factors determining it. Materials and methods. To achieve the purpose, water quality monitoring data on the Priplotinny Reach of the Kuibyshev Reservoir in the period 2018-2022 were used. Water samples were taken monthly from the surface horizon (0,5 m). Laboratory chemical analysis of water was carried out in accordance with current regulatory documents. Results and discussion. Intra-annual fl uctuations in the average monthly values of DOM content are: for biochemical oxygen consumption (BOD5 ) 1.5-2.2 mgO2 /dm3 , for permanganate oxidation (PO) – 7.0-8.6 mgO2 /dm3 , for bichromate oxidation (BO) – 23-28 mgO2 /dm3 . The DOM content is characterised by well-defi ned seasonal variability and includes four periods (I, II, III and IV), which diff er in duration and multidirectional trends. In period I, the DOM content gradually increases from January to May. Period II is characterised by a decrease in DOM content and lasts from mid-May to mid-June during the spring fl ood. In period III, the DOM content increases signifi cantly under the infl uence of the process of mass development of cyanobacteria (MDC). In period III, the DOM content gradually decreases during the autumn and winter low water periods. In a seasonal context, the highest DOM content is observed in summer low water, when the MRC process is actively occurring. As a result, the content of DOM in July–August increases within the framework of BOD5 by 20-25 %, within the framework of PO – by 13-15 %, within the framework of BO – by 4-6 %. The degree of infl uence of the MRC process on the DOM content depends on weather conditions. The problem of increasing DOM content is aggravated in hot and dry years, when the MRC process is activated in the reservoir, which signifi cantly increases the content of easily oxidized DOM in the water. Conclusions. The high content of DOM signifi cantly complicates the use of the Kuibyshev reservoir for domestic drinking water supply and fi sheries. In the future, the problem of deterioration in water quality will only worsen due to an increase in nutrient load, climate warming and the intensifi cation of the MRC process.